The combination of an internal combustion engine and a generator to produce electrical power has been known for many years. Relatively more recently, however, engine-driven generators have been used in electrically powered mobile machines to provide electrical power for propulsion and operation of other machine systems. In such strategies, rather than requiring relatively rapid ramp-up and down of engine output to accommodate changes in power demand, relatively more stable, smooth operation and transition across an engine power output range may be achieved. In other words, by powering some or all of the machine systems with electrical power provided by an on-board engine and generator system, combustion characteristics and overall engine operation can be more predictable and changes less rapidly. This allows wide and rapid swings in engine speed and load associated with changes in power demand on the system to be avoided. Where engine operation is more predictable, and changes in engine output more gradual, superior control over emissions and other factors such as fuel efficiency has been demonstrated as compared to traditional designs where an engine directly powered the machine propulsion system, hydraulics, etc.
In many machine systems where an engine directly drives a generator, vibrations and inertia associated with system operation can be transmitted between the engine and the generator. This can be particularly problematic where the generator inertia is fairly close to that of the engine. In some instances, resonance vibrations in the system can result in significant torque spikes within the system, at minimum wasting energy and roughening operation, and in certain instances even damaging components. While some system designs are sufficiently robust to withstand torque spikes when accelerating or decelerating through a speed range where resonance vibrations tend to occur, these systems can have other drawbacks, such as higher weight and cost.
One example of a machine having electrical power system is disclosed and co-owned U.S. Pat. No. 7,547,981. This reference teaches a drive coupling that allows some relative slip between rotation of the engine and rotation of the generator in order to accommodate resonance vibrations, such as those that might occur at engine start up. One potential problem associated with the machine of the '981 patent relates to the possibility of the drive coupling assembly not being properly centered. In such an instance, there is a potential for increased spring failure and wear, and increased bearing loading due to an eccentric relationship between the rotating engine and rotating generator.
The present disclosure is directed to one or more of the problems or shortcomings set forth above.